1. Field of the Invention
This invention relates to powered torque-applying tools, and more specifically, to control methods for such power tools.
2. Description of Related Art
Computer-controlled, torque-applying power tools (e.g., fluid or electric powered tools) are typically used in production environments to secure threaded fasteners (e.g., nuts and bolts) into joints. Such power tools are typically coupled to a controller. The tool usually has a high-speed, high-torque motor coupled to a universal adapter head. Various interchangeable bits (e.g., bits appropriate for hex-head bolts and hexagonal nuts) are connected to the head in order to drive threaded fasteners.
The controller controls the power supply (e.g. fluid or electricity) for each handheld unit, and also monitors such parameters as the instantaneous tool speed and instantaneous applied torque. In a typical fastening job, fasteners are tightened to a predetermined, specified torque. As the handheld units operate at high speed, on the order of several hundred RPM or higher, the controller is typically used to control and stop the motor of the tool automatically so that the torque applied to the fastener and joint does not exceed the specified torque. A fastening cycle is initiated by the user's activation of an ON switch in the case of a hand-held tool, or by the controller in the case of a robotic tool. However, in view of the high speed of the tool, overshoot (exceeding the intended torque) is a common problem.
U.S. Pat. Nos. 5,215,270, 5,315,501, 5,519,614, 5,637,968, 5,650,574, and 6,516,896 disclose various conventional fastening tool controllers designed to control a tool's torque while avoiding overshoot.